EVALUATION OF A FIRST-ORDER MODEL FOR THE PREDICTION OF THE BIOACCUMULATION OF PCBS AND DDT FROM SEDIMENT INTO THE MARINE DEPOSIT-FEEDING CLAM MACOMA-NASUTA

A first-order model for predicting contaminant bioaccumulation from se diments into benthic invertebrates was validated using a marine deposi t-feeding clam, Macoma nasuta, exposed to polychlorobiphenyl (PCB)-spi ked and dichlorodiphenyltrichloroethane (DDT)-contaminated sediments. Contaminant uptake and depuration were analyzed following short-term a nd long-term sediment exposures. Uptake and depuration rates were used to predict steady-state bioaccumulation factors (BAFs) and exposure t imes needed to attain steady state. These predictions were compared to observed steady-state BAFs. Estimating elimination and uptake rates f rom depuration and shea-term uptake experiments was an accurate means of predicting BAFs for some PCBs (log octanol-water partition coeffici ent, K-ow, <7) but was not as accurate for predicting DDT BAFs. The ex posure time need to attain steady state was poorly predicted by the mo del. The results demonstrated that a standard 28-d bioaccumulation tes t estimated steady-state tissue residues within two-fold and was a bet ter predictor than the model for the BAFs of superlipophilic PCBs (log K-ow >7). Differences in contaminant bioavailability were noted betwe en field-contaminated (DDT) and laboratory-spiked (PCB) sediments.